Optical fiber connecting element and alignment sleeve

ABSTRACT

It is an object of the present invention to enable quick, easy, and inexpensive connections even in a narrow area using an inexpensive device and an inexpensive optical fiber connecting element, thereby achieving high operability and high durability reliability. An optical fiber connecting element includes an optical alignment sleeve having tapered insertion ports formed at opposite ends thereof and having an ejection port opened in an area in which the two optical fibers inserted through the insertion ports are butted against each other, a cyanoacrylate-type glue injected into the insertion ports and the injection port to fix the two optical fibers, and a heat-shrinkable tube wrapped around the optical alignment sleeve and two optical fiber coatings and having a hot-melt adhesive provided therein.

[0001] This application is based on Japanese Patent Application Nos.2001-338296 filed Nov. 2, 2001 and 2002-081957 filed Mar. 22, 2002, thecontents of which are incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an optical fiber connectingelement, an optical alignment sleeve, an optical fiber connectingmethod, and an optical fiber connecting device, and more specifically,to a method of fixedly connecting an optical fiber using an opticalalignment sleeve filled with an adhesive.

[0004] 2. Description of the Related Art

[0005] In laying an optical fiber cable, for example, a cable of unitlength 2 km is laid in each section. Cables in two sections areconnected together by connecting optical fibers in the cable in one ofthe sections to the corresponding optical fibers in the cable in theother section using a connection box called a “closure”. A cable forlong-distance transmissions requires a large number of closures, and amulticore cable requires optical fibers to be connected together a hugenumber of times. Accordingly, it is necessary to be able to connectoptical fibers together more precisely and to reduce the number of timesthat the optical fibers are connected together, thereby achievinginexpensive and reliably durable optical-fiber connections.

[0006] Conventionally known methods of connecting optical fiberstogether include (1) heating and melting the optical fibers, i.e.so-called fusion splicing, (2) mechanically fixing the optical fibers ina connection box, i.e. so-called mechanical splicing, and (3) usingtransparent sleeves or V-type grooves with transparent covers to buttthe optical fibers against each other and using an UV-curable adhesiveto fixedly connect the optical fibers together, i.e. so-called adhesivesplicing.

[0007] However, the fusion splicing requires an expensive fusionsplicer, which is large and does not allow connections to be carried outeasily in a narrow area. Another problem with the fusion splicing isthat the optical fibers require an extra length sufficient to allow thefibers to be set in the fusion splicer and an extra length for areconnection carried out if the fusion fails.

[0008] The mechanical splicing requires more inexpensive connectiontools than the fusion splicing but requires an expensive connectionelement, a mechanical splice container, thereby increasing costs perconnection. Another problem with the mechanical splicing is that thefixation of the optical fibers rely on mechanical clamping force,thereby degrading durability reliability.

[0009] Problems with the adhesive splicing are that UV irradiation,which involves high costs, are required and that ultraviolet rays areharmful to human bodies, resulting in degraded operability at theworking site.

SUMMARY OF THE INVENTION

[0010] It is an object of the present invention to provide an opticalalignment sleeve and an optical fiber connecting element that enablequick, easy, and inexpensive connections even in a narrow area, therebyachieving high operability and high durability reliability, and toprovide an optical fiber connecting method and apparatus used for theoptical alignment sleeve and the optical fiber connecting element.

[0011] To attain this object, an optical fiber connecting elementcomprises an optical alignment sleeve having tapered insertion portsformed at opposite ends thereof and through which optical fibers areinserted and having an ejection port opened in an area in which the twooptical fibers inserted through the insertion ports are butted againsteach other, a cyanoacrylate-type glue injected into the insertion portsand the injection port to fix the two optical fibers, and aheat-shrinkable tube wrapped around the optical alignment sleeve and thetwo optical fibers and having a hot-melt adhesive provided therein.

[0012] Also an optical fiber connecting element may comprise an opticalalignment sleeve having tapered insertion ports formed at opposite endsthereof and through which optical fibers are inserted and having anejection port opened in an area in which the two optical fibers insertedthrough the insertion ports are butted against each other, acyanoacrylate-type glue injected into the insertion ports and theinjection port to fix the two optical fibers, a reinforcing tube wrappedaround the optical alignment sleeve and the two optical fibers, and sealmaterials that fix the two optical fibers and the reinforcing tube atopposite ends of the reinforcing tube.

[0013] Further, an optical fiber connecting method comprises a firststep of inserting two optical fibers into an optical alignment sleeveand butting the optical fibers against each other, the optical alignmentsleeve having tapered insertion ports formed at opposite ends thereofand through which optical fibers are inserted and having an ejectionport opened in an area in which the two optical fibers inserted throughthe insertion ports are butted against each other, a second step ofinjecting a cyanoacrylate-type adhesive into the insertion ports and theinjection port to fix the two optical fibers, and a third step ofwrapping a heat-shrinkable tube having a hot-melt adhesive providedinside, around the optical alignment sleeve and the two optical fibersand heating the heat-shrinkable tube to fix the optical alignment sleeveand the two optical fibers.

[0014] Furthermore, an optical fiber connecting method may comprise thesteps of: inserting two optical fibers into an optical alignment sleeveand butting the optical fibers against each other, the optical alignmentsleeve having tapered insertion ports formed at opposite ends thereofand through which optical fibers are inserted and having an ejectionport opened in an area in which the two optical fibers inserted throughthe insertion ports are butted against each other, injecting acyanoacrylate-type adhesive into the insertion ports and the injectionport to fix the two optical fibers, and wrapping a reinforcing tubearound the optical alignment sleeve and the two optical fibers and usingseal materials to fix the two optical fibers at opposite ends of thereinforcing tube.

[0015] An optical alignment sleeve for optical fibers which allows twooptical fibers to be butted against each other for connection, theoptical alignment sleeve comprises tapered insertion ports through whichoptical fibers are inserted, and holding sections each having a grooveformed therein to allow the optical fiber inserted through the insertionport to discharge an extra portion of an adhesive already filled in theoptical alignment sleeve, to the insertion ports, and wherein theoptical fibers inserted through the insertion ports allow the extraportion of the adhesive discharged to the insertion ports to formfillets.

[0016] Also the optical alignment sleeve may comprise tapered insertionports through which optical fibers are inserted, and holding sectionseach having a drain section formed therein so that the optical fiber areinserted through the insertion port to discharge an extra portion of anadhesive already filled in the optical alignment sleeve, to theinsertion ports, and wherein the optical fibers are inserted through theinsertion ports to allow the extra portion of the adhesive discharged tothe insertion ports to form fillets.

[0017] An optical fiber connecting method comprises a first step ofinserting optical fibers into an optical alignment sleeve to dischargean extra portion of an adhesive already filled into holding sections ofthe optical alignment sleeve, to insertion ports formed at opposite endsof the optical alignment sleeve, via grooves formed in the holdingsections, a second step of inserting the optical fibers into the opticalalignment sleeve to allow the extra portion of the adhesive dischargedto the tapered insertion ports to form fillets, and a third step ofsolidifying the adhesive to fix the optical alignment sleeve and theoptical fibers.

[0018] Also an optical fiber connecting method comprise a first step ofinserting optical fibers into an optical alignment sleeve to dischargean extra portion of an adhesive already filled into holding sections ofthe optical alignment sleeve, to insertion ports formed at opposite endsof the optical alignment sleeve, via grooves formed in the holdingsections, a second step of inserting the optical fibers into the opticalalignment sleeve to allow the extra portion of the adhesive dischargedto the tapered insertion ports to form fillets, and a third step ofsolidifying the adhesive to fix the optical alignment sleeve and theoptical fibers.

[0019] An optical fiber connecting device comprises optical alignmentsleeve holding means for fixing an optical alignment sleeve, and opticalfiber holding means having a clamp that fixes optical fibers in V-typegroove and means for moving the clamp so as to allow the optical fibersto be inserted into the optical alignment sleeve and butted against eachother therein, and wherein the clamp has a fixed cover that can beclosed with the optical fibers temporarily fixed in the V-type grooveformed in a clamp base, using one of the fingers, and the optical fibersare sandwiched between the clam base and the fixed cover in the V-typegroove.

[0020] The above and other objects, effects, features and advantages ofthe present invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1A is a perspective view showing an optical alignment sleeveaccording to a first embodiment of the present invention;

[0022]FIG. 1B is a sectional view showing the optical alignment sleeveaccording to the first embodiment of the present invention;

[0023]FIG. 2 is a sectional view showing a method of fixing opticalfibers using an optical fiber connecting element;

[0024]FIG. 3 is a sectional view showing an optical fiber connectingelement according to the first embodiment of the present invention;

[0025]FIG. 4 is a sectional view showing an optical fiber connectingelement according to a second embodiment of the present invention;

[0026]FIG. 5 is a sectional view showing an optical fiber connectingelement according to a third embodiment of the present invention;

[0027]FIG. 6 is a sectional view showing an optical alignment sleeveaccording to the second embodiment of the present invention;

[0028]FIG. 7 is a transverse sectional view of a central portion of theoptical alignment sleeve according to the second embodiment of thepresent invention;

[0029]FIG. 8 is a sectional view showing a method of fixing opticalfibers using the optical alignment sleeve;

[0030]FIG. 9 is a sectional view showing an optical alignment sleeveaccording to the third embodiment of the present invention;

[0031]FIG. 10 is a transverse sectional view of a central portion of theoptical alignment sleeve according to the third embodiment of thepresent invention;

[0032]FIG. 11 is a sectional view showing an optical alignment sleeveaccording to a fourth embodiment of the present invention;

[0033]FIG. 12A is a plan view showing an optical fiber connecting deviceaccording to one embodiment of the present invention;

[0034]FIG. 12B is a side view showing the optical fiber connectingdevice according to the embodiment of the present invention shown inFIG. 12A;

[0035]FIG. 13A is a diagram showing a V-type groove clamp of the opticalfiber connecting device according to the embodiment of the presentinvention shown in FIG. 12A;

[0036]FIG. 13B is a side view showing how the optical fibers are fixedin the V-type groove clamp;

[0037]FIG. 14A is a plan view showing a method of fixing the opticalfibers in the V-type groove clamp; and

[0038]FIG. 14B is a plan view showing the V-type groove clamp with theoptical fibers fixed therein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Embodiments of the present invention will be described below indetail with reference to the drawings.

[0040] First Embodiment of Optical Alignment Sleeve

[0041] The principle of a first embodiment of an optical alignmentsleeve is that optical fibers are butted against each other in anoptical alignment sleeve having an inner diameter 1 to 1 μm larger thanthe outer diameter of an optical fiber, and are fixedly connectedtogether using cyanoacrylate-type glue. Furthermore, to improveintensity and durability reliability, a heat-shrinkable tube containinga hot-melt adhesive or a reinforcing tube and a seal material are usedfor packaging.

[0042]FIGS. 1A and 1B show an optical alignment sleeve according to afirst embodiment of the present invention. An optical alignment sleeve11 is used to butt optical fibers to be connected together, against eachother. The optical alignment sleeve 11 has tapered insertion ports 12and a guide section 14 which is contiguous to the insertion ports 12 andwhich has an inner diameter 1 to 2 μm larger than the outer diameter ofthe optical fibers. Further, the optical alignment sleeve 11 has, in acentral portion of the sleeve, an injection port 13 through which anadhesive is injected to butt the optical fibers against each other inthe center of the sleeve.

[0043] The optical alignment sleeve may be made of glass, metal, orplastics such as polyphenylene sulfide or liquid polymer, which has asmall thermal expansion coefficient.

[0044]FIG. 2 shows a method of fixing optical fibers using the opticalalignment sleeve. Single-mode optical fibers 21 a and 21 b having anouter diameter of 0.125 mm are inserted into the optical alignmentsleeve 11 made of glass and having an outer diameter of 0.127 mm and anouter diameter of 1.8 mm, and are butted against each other in theinjection port 13. Ethyl cyanoacrylate instant glue is injected throughthe insertion ports 12 and the injection port 13 to fixedly connect thesingle-mode optical alignment fibers 21 a and 21 b together.

[0045] The cyanoacrylate glue is expressed by:

[0046] where R denotes C_(n)H2_(n+1) (n is a positive integer between 1and 16), i-butyl, i-propyl, or i-pentyl.

[0047] First Embodiment of Optical Fiber Connecting Element

[0048]FIG. 3 shows an optical fiber connecting element according to thefirst embodiment of the present invention. A heat-shrinkable tube 41 anda reinforcing rod 42 are used to further reinforce the single-modeoptical fibers 21 a and 21 b fixed in the optical alignment sleeve 11using cyanoacrylate glue 31. The optical alignment sleeve 11, in whichthe optical fibers have been butted against each other are covered withthe heat-shrinkable tube 41, already inserted through optical fibercoatings 22 a and 22 b. The heat-shrinkable tube 41 contains areinforcing rod 42 and a hot-melt adhesive 43. Then, the heat-shrinkabletube 41 is heated to integrate the optical alignment sleeve 11 with theoptical fiber coatings 22 a and 22 b for reinforcement.

[0049] The hot-melt adhesive 43 is a silane-grafted ethylene copolymerhot-melt adhesive shaped like a tube having an inner diameter of 2.0 mm,an outer diameter of 2.5 mm, and a length of 60 mm. The hot-metaladhesive 43 is provided inside the heat-shrinkable tube. Alternatively,a hot-melt adhesive may be applied to the inner surface of theheat-shrinkable tube. The hot-melt adhesive may be a high-durabilityEVA-type polymer, e.g. a high function polymer (trade name: HPR)commercially available from Mitusi Du Pont Polychemical Company.

[0050] The reinforcing rod 42 is a round bar made of metal, morespecifically SUS and having an outer diameter of 1.2 mm and a length of60 mm. The heat-shrinkable tube 41 is made of polyethylene and having aninner diameter of 4.2 mm, an outer diameter of 4.4 mm, a length of 60mm, and a shrinkage factor of 40 to 50%.

[0051] In this case, the single-mode optical fibers 21 a and 21 bexhibited an insertion loss of 0.02 dB or less at a wavelength of 1.5μm. In temperature cycling tests at −20 to +60° C., an optical fiberconnected portion exhibited an optical loss change of 0.2 dB or less.The optical fiber connected portion had a peel strength of 2.3 kg andmaintained a strength of 2 kg or more even after the fibers had beenimmersed in 60° C. water for two weeks.

[0052] Other implementation

[0053] The single-mode optical fibers 21 a and 21 b having an outerdiameter of 0.125 mm are inserted into the optical alignment sleeve 11made of polyphenylene sulfide and having an inner diameter of 0.127 mm,an outer diameter of 2 mm, and a length of 20 mm, and are butted againsteach other in the injection port 13. A high viscous propyl cyanoacrylateinstant glue is injected into the insertion ports 12 to fixedly connectthe single-mode optical fibers 21 a and 21 b together. Silicone-typematching oil is injected into the injection port 13. The injection port13 is 0.2 mm in width. The insertion ports 12 have an inner diameter of1.4 mm on a side thereof through which the optical fibers are inserted,and have an inner diameter of 0.127 μm at the boundary between eachinsertion port and the guide section 14. The thus fixed single-modeoptical fibers 21 a and 21 b are reinforced with the heat-shrinkabletube 41 and the reinforcing rod 42.

[0054] In this case, the single-mode optical fibers 21 a and 21 bexhibited an insertion loss of 0.05 dB or less at a wavelength of 1.5μm. In temperature cycling tests at −20 to +60° C., an optical fiberconnected portion exhibited an optical loss change of 0.1dB or less. Theoptical fiber connected portion had a peel strength of 2 kg andmaintained a strength of 2 kg or more even after the fibers had beenimmersed in 60° C. water for two weeks.

[0055] Second Embodiment of Optical Fiber Connecting Element

[0056]FIG. 4 shows an optical fiber connecting element according to asecond embodiment of the present invention. The single-mode opticalfibers 21 a and 21 b having an outer diameter of 0.125 mm are insertedinto the optical alignment sleeve 11 made of glass and having an innerdiameter of 0.127 mm, an outer diameter of 1.8 mm, and a length of 20mm, and are butted against each other in the injection port 13. An ethylcyanoacrylate instant glue is injected through the insertion ports 12and the injection port 13 to fixedly connect the single-mode opticalfibers 21 a and 21 b together. The optical alignment sleeve 11 in whichthe optical fibers have been butted against each other is covered withthe heat-shrinkable tube 41. Then, the heat-shrinkable tube 41 is heatedto integrate the optical alignment sleeve 11 with the optical fibercoatings 22 a and 22 b for reinforcement.

[0057] The heat shrinkable tube 41 contains a stepped reinforcing rod 44and a hot-melt adhesive 43. The stepped reinforcing rod is moreinexpensive and easier to handle when it is made of iron so as to beround. The reinforcing rod has a recessed central portion which contactswith the optical alignment sleeve. The central portion is recessed toform a step because this hinders stress induced by thermal expansion orcontraction of the hot-melt adhesive or heat shrinkable tube from actingon portions of the optical fibers located near the inlet and outlet ofthe optical alignment sleeve when the hot-melt adhesive is cooled or thetemperature of the operating environment changes.

[0058] In this case, the single-mode optical fibers 21 a and 21 bexhibited an insertion loss of 0.01 dB or less at a wavelength of 1.5μm. In temperature cycling tests at −20 to +60° C., an optical fiberconnected portion exhibited an optical loss change of 0.1 dB or less.The optical fiber connected portion had a peel strength of 2 kg andmaintained a strength of 2 kg or more even after the fibers had beenimmersed in 60° C. water for two weeks.

[0059] Third Embodiment of Optical Fiber Connecting Element

[0060]FIG. 5 shows an optical fiber connecting element according to athird embodiment of the present invention. The single-mode opticalfibers 21 a and 21 b having an outer diameter of 0.125 mm are insertedinto the optical alignment sleeve 11 made of glass and having an innerdiameter of 0.127 mm, an outer diameter of 1.8 mm, and a length of 20mm, and are butted against each other in the injection port 13. An ethylcyanoacrylate glue is injected through the insertion port 12 and theinjection ports 13 to fixedly connect the single-mode optical fibers 21a and 21 b together. The optical alignment sleeve 11, in which theoptical fibers are butted against each other, is covered with areinforcing tube 51 already inserted through the optical fiber coatings22 a and 22 b. Then, a room temperature setting moisture-proof sealmaterials 52 are provided at the respective ends of the reinforcing tube51 to bond the reinforcing tube 51 and the optical fiber coatings 22 aand 22 b together to seal the reinforcing tube 51.

[0061] The reinforcing tube 51 is a pipe made of stainless steel andhaving an outer diameter of 3 mm and an inner diameter of 1.6 mm. Thereinforcing tube made of metal, particularly stainless steel isdifficult to rotten and is inexpensive.

[0062] In this case, the single-mode optical fibers 21 a and 21 bexhibited an insertion loss of 0.02 dB or less at a wavelength of 1.5μm. In temperature cycling tests at −20 to +60° C., the optical fiberconnected portion exhibited an optical loss change of 0.1dB or less. Theoptical fiber connected portion had a peel strength of 1.5 kg andmaintained a strength of 1 kg or more even after the fibers had beenimmersed in 60° C. water for two weeks.

[0063] Second Embodiment of Optical Alignment Sleeve

[0064] The principle of a second embodiment of the optical alignmentsleeve is that an adhesive is filled beforehand into an opticalalignment sleeve having an inner diameter 1 to 2 μm larger than theouter diameter of the optical fibers and that the optical fibers arethen inserted through tapered insertion ports located at the respectiveends of the optical alignment sleeve and are butted against each otherand fixedly connected together. When the optical fibers are inserted, anextra portion of the adhesive is moved to the opposite ends of theoptical alignment sleeve through a drain ditch to fix the opticalfibers, optical fiber coatings, and optical alignment sleeve together,thereby sealing the optical fibers.

[0065]FIG. 6 shows an optical alignment sleeve according to the secondembodiment of the present invention. An optical alignment sleeve 61 iscomposed of tapered insertion ports 62 a and 62 b through which theoptical fibers 21 a and 21 b are inserted, larger-diameter holdingsections 63 a and 63 b in which the optical fiber coatings 22 a and 22 bare held, and a smaller-diameter holding section 64 in which the opticalfibers 21 a and 21 b are held. The optical alignment sleeve 61 may bemade of glass, metal, or plastics such as polyphenylene sulfide orliquid polymer, which has a small thermal expansion coefficient.

[0066]FIG. 7 is a transverse sectional view of a central portion of theoptical alignment sleeve. This is a transverse sectional view of thesmaller-diameter holding section 64, taken along line VII-VII in FIG. 6.The smaller-diameter holding section 64 has a rectangle drain ditch 65through which the adhesive is discharged. The drain ditch 65 iscontinuously formed in the larger-diameter holding sections 63 a and 63b and is connected to the insertion ports 62 a and 62 b.

[0067]FIG. 8 shows a method of fixing optical fibers using the opticalalignment sleeve. When the optical fibers are inserted, an extra portionof an adhesive 66 is moved to the insertion ports 62 a and 62 b of theoptical alignment sleeve through the drain ditch 65 to fix the opticalfibers 22 a and 22 b and the optical alignment sleeve 61 together in thetapered insertion ports 62 a and 62 b, thereby sealing the opticalfibers. The insertion ports 62 a and 62 b are tapered so as to allow theoptical fibers 21 a and 21 b to be inserted thereinto and are adapted toallow the extra portion of the adhesive 66 to form a sufficient fillet.

[0068] Third Embodiment of Optical Alignment Sleeve

[0069]FIG. 9 shows an optical alignment sleeve according to a thirdembodiment of the present invention. An optical alignment sleeve 71 iscomposed of tapered insertion ports 72 a and 72 b through which theoptical fibers 21 a and 21 b are inserted, larger-diameter holdingsections 73 a and 73 b in which the optical fiber coatings 22 a and 22 bare held, and a smaller-diameter holding section 74 in which the opticalfibers 21 a and 21 b are held.

[0070]FIG. 10 is a transverse sectional view of a central portion of theoptical alignment sleeve. This is a transverse sectional view of thesmaller-diameter holding section 74, taken along line X-X in FIG. 9. Thesmaller-diameter holding section 74 has a drain hole 75 through whichthe adhesive is discharged. Instead of the drain hole 75, a drain slitmay be formed over a vertical cross section of the optical alignmentsleeve. When the optical fibers are inserted, an extra portion of theadhesive is moved to the drain hole 75, a drain section, to fix theoptical fibers and the optical alignment sleeve together, therebysealing the optical fibers.

[0071] The adhesive 66 has a viscosity of 10,000 cP or has its viscosityadjusted so as to be gelated so that even after it has been filled intothe optical alignment sleeve 61 or 71, it will not flow out before theoptical fibers 21 are inserted or be scattered easily when the opticalfibers 21 are inserted.

[0072] The adhesive 66 is of an ultraviolet curing type or a visiblelight curing type. The optical alignment sleeves 61 and 71 are composedof plastics, glass, or zirconia, through which ultraviolet rays orvisible light can be transmitted. After the optical fibers have beeninserted into the optical alignment sleeve 61 or 71, the adhesive 66 issolidified using ultraviolet rays or visible light. Further, if theoptical alignment sleeve 61 or 71 is composed of nondeforming steel, theadhesive 66 should be of a heat-hardening type.

[0073] Four Embodiment of Optical Alignment Sleeve

[0074]FIG. 11 shows an optical alignment sleeve according to a fourthembodiment of the present invention. An optical alignment sleeve 81contains a reinforcing rod 87 in addition to the arrangements of theoptical alignment sleeve 61 according to the second embodiment, shown inFIG. 6. Further, durability or strength can be increased by buttingoptical fibers against each other and then covering the optical fibersand the optical alignment sleeve with a heat-shrinkable tube.

[0075] Embodiment of Optical Fiber Connecting Device

[0076]FIG. 12A is a plan view of an optical fiber connecting deviceaccording to one embodiment of the present invention. FIG. 12B is a sideview of the optical fiber connecting device. An optical fiber connectingdevice 100 comprises a base 101, optical fiber holding sections 102 aand 102 b that fix the optical fibers 21 a and 21 b, an opticalalignment sleeve holding section 103 that fixes the optical alignmentsleeve 61, 71, or 81, and a rotatable microscope 104 that enablesmagnification of a connection area in which the optical fibers 21 a and21 b are butted against each other, the optical fiber holding sections102 a and 102 b, optical alignment sleeve holding section 103, androtatable microscope 104 all being arranged on the base 101. The opticalfiber holding sections 102 a and 102 b each comprise a V-type grooveclamps 121 a or 121 b, respectively, which can be moved in the directionof optical axis of the fixed optical fiber by a fine-tuning screw 122 aor 122 b, respectively.

[0077] Description will be give of a method of connecting optical fiberstogether using an optical fiber connecting device 100. The opticalalignment sleeve 61, 71, or 81 with the adhesive 66 filled therein isfixed to a splicer clamp 131 of the optical alignment sleeve holdingsection 103. Coated portions at the tips of the optical fibers 21 a and21 b are removed. Then, the optical fibers 21 a and 21 b are fixed inthe V type groove clamps 121 a and 121 b of the optical fiber holdingsections 102 a and 102 b, respectively. The fine-tuning screws 122 a and122 b are used to move the V type groove clamps 121 a and 121 b,respectively, to insert the optical fibers 21 a and 21 b, respectively,into the optical alignment sleeve 61, 71, or 81. The rotatablemicroscope 104 is used to confirm that the end surfaces of the left andright optical fibers 21 a and 21 b. Then, the adhesive 66 is solidified.

[0078]FIG. 13A shows the configuration of the V-type groove clamp of theoptical fiber connecting device. The V-type groove clamp 121 is composedof a clamp base 124 having a V-type groove 122 formed therein and inwhich the optical fibers are placed, and a fixed cover 123 fixed by theclamp base 124 and a hinge. FIG. 13A shows that the fixed cover 123 isopen, and FIG. 13B shows that the fixed cover 123 is closed to fix theoptical fiber in the V-type groove 122.

[0079]FIG. 14A shows a method of fixing the optical fibers in the V-typegroove. The optical fiber coating 22 is not sufficiently straightbecause it is coiled repeatedly. However, the optical fiber 21, fromwhich the coated portion has been removed using a tool called a“remover”, is adequately straight. Thus, only the tip of the opticalfiber 21, i.e. a bare portion of the optical fiber, is projected fromone end of the V-type groove clamp 121. Then, the optical fiber 21 isfixed in the V-type groove 122. At this time, the optical fiber 21 istemporarily fixed using one finger (as shown in FIG. 14A). Subsequently,with the optical fiber 21 remaining fixed in this manner, the fixedcover 123 is closed to fix the optical fiber 21 without using the finger(as shown in FIG. 14B).

[0080] The optical fiber 21 is thus fixed in the V-type groove 122 whileusing one finger for temporary fixation, thereby allowing only the bareoptical fiber to be guided to the insertion ports 62 or 72 of theoptical alignment sleeve 61, 71, or 81, respectively.

[0081] The present invention will be described below in further detailon the basis of examples. However, it should be appreciated that thepresent invention is not limited to these example.

EXAMPLE 1

[0082] To connect single-mode optical fibers of outer diameter 0.125 mmtogether, a transparent polycarbonate resin is used to produce anoptical alignment sleeve 61, shown in FIG. 6, by injection molding. Theoptical alignment sleeve 61 had an inner diameter of 0.127 mm, an outerdiameter of 4 mm, and a length of 30 mm and had a 50×100 μm drain ditch65 formed inside. The optical alignment sleeve 61 is filled with anultraviolet curing type acrylic-type adhesive having its viscosityadjusted to 20,000 cP.

[0083] The optical fibers 21 a and 21 b were inserted into the opticalalignment sleeve 61 and the ends thereof were butted together. Then, theadhesive 66 filled into the optical alignment sleeve moved from thedrain ditch 65 to the tapered insertion ports 62 a and 62 b to form afillet between the optical fiber coating 22 and the optical alignmentsleeve 61. The optical alignment sleeve was irradiated with ultravioletrays (365 nm) having a quantity of light of 100 mW/cm³, for 60 secondsto solidify the adhesive.

[0084] In this case, the single-mode optical fibers 21 a and 21 bexhibited an insertion loss of 0.03 dB or less at a wavelength of 1.5μm. In temperature cycling tests at −20 to +60° C., the optical fiberconnected portion exhibited an optical loss change of 0.2 dB or less.The optical fiber connected portion had a peel strength of 2 kg andmaintained a strength of 2 kg or more even after the fibers had beenimmersed in 60° C. water for two weeks.

EXAMPLE 2

[0085] To connect single-mode optical fibers of outer diameter 0.125 mmtogether, nondeforming steel having a coefficient of linear expansion of6×10⁻⁷/° C. was used to produce an optical alignment sleeve 61, shown inFIG. 6, powder molding. The optical alignment sleeve 61 had an innerdiameter of 0.127 mm, an outer diameter of 4 mm, and a length of 30 mmand had a 50×100 μm drain ditch 65 formed inside. The optical alignmentsleeve 61 was filled with a heat-hardening type epoxy-type adhesivehaving its viscosity adjusted to 20,000 cP.

[0086] The optical fibers 21 a and 21 b were inserted into the opticalalignment sleeve 61 and the ends thereof were butted together. Then, theadhesive filled into the optical alignment sleeve moved from the drainditch 65 to the tapered insertion ports 62 a and 62 b to form a filletbetween the optical fiber coating 22 and the optical alignment sleeve61. The optical alignment sleeve was heated at 120° C. for two minutesto solidify the adhesive.

[0087] In this case, the single-mode optical fibers 21 a and 21 bexhibited an insertion loss of 0.03 dB or less at a wavelength of 1.5μm. In temperature cycling tests at −20 to +60° C., the optical fiberconnected portion exhibited an optical loss change of 0.2 dB or less.The optical fiber connected portion had a peel strength of 2 kg andmaintained a strength of 2 kg or more even after the fibers had beenimmersed in 60° C. water for two weeks.

[0088] The present invention has been described in detail with respectto preferred embodiments, and it will now be apparent from the foregoingto those skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspects, and it isthe intention, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

What is claimed is:
 1. An optical fiber connecting element comprising:an optical alignment sleeve having tapered insertion ports formed atopposite ends thereof and through which optical fibers are inserted andhaving an ejection port opened in an area in which the two opticalfibers inserted through the insertion ports are butted against eachother; a cyanoacrylate-type glue injected into said insertion ports andsaid injection port to fix said two optical fibers; and aheat-shrinkable tube wrapped around said optical alignment sleeve andsaid two optical fibers and having a hot-melt adhesive provided therein.2. An optical fiber connecting element according to claim 1, furthercomprising a reinforcing rod inserted into said hot-melt tube.
 3. Anoptical fiber connecting element according to claim 2, wherein saidreinforcing rod has a recess in an area in which said reinforcing rodcontacts with said optical alignment sleeve.
 4. An optical fiberconnecting element comprising: an optical alignment sleeve havingtapered insertion ports formed at opposite ends thereof and throughwhich optical fibers are inserted and having an ejection port opened inan area in which the two optical fibers inserted through the insertionports are butted against each other; a cyanoacrylate-type glue injectedinto said insertion ports and said injection port to fix said twooptical fibers; a reinforcing tube wrapped around said optical alignmentsleeve and said two optical fibers; and seal materials that fix said twooptical fibers and said reinforcing tube at opposite ends of thereinforcing tube.
 5. An optical fiber connecting method comprising: afirst step of inserting two optical fibers into an optical alignmentsleeve and butting the optical fibers against each other, the opticalalignment sleeve having tapered insertion ports formed at opposite endsthereof and through which optical fibers are inserted and having anejection port opened in an area in which the two optical fibers insertedthrough the insertion ports are butted against each other; a second stepof injecting a cyanoacrylate-type adhesive into said insertion ports andsaid injection port to fix said two optical fibers; and a third step ofwrapping a heat-shrinkable tube having a hot-melt adhesive providedinside, around said optical alignment sleeve and said two optical fibersand heating the heat-shrinkable tube to fix said optical alignmentsleeve and said two optical fibers.
 6. An optical fiber connectingmethod according to claim 5, wherein said third step includes a step ofinserting a reinforcing rod into said heat-shrinkable tube.
 7. Anoptical fiber connecting method comprising the steps of: inserting twooptical fibers into an optical alignment sleeve and butting the opticalfibers against each other, the optical alignment sleeve having taperedinsertion ports formed at opposite ends thereof and through whichoptical fibers are inserted and having an ejection port opened in anarea in which the two optical fibers inserted through the insertionports are butted against each other; injecting a cyanoacrylate-typeadhesive into said insertion ports and said injection port to fix saidtwo optical fibers; and wrapping a reinforcing tube around said opticalalignment sleeve and said two optical fibers and using seal materials tofix said two optical fibers at opposite ends of the reinforcing tube. 8.An optical alignment sleeve for optical fibers which allows two opticalfibers to be butted against each other for connection, the opticalalignment sleeve comprising: tapered insertion ports through whichoptical fibers are inserted; and holding sections each having a grooveformed therein to allow said optical fiber inserted through theinsertion port to discharge an extra portion of an adhesive alreadyfilled in the optical alignment sleeve, to said insertion ports, andwherein said optical fibers inserted through said insertion ports allowthe extra portion of said adhesive discharged to said insertion ports toform fillets.
 9. An optical alignment sleeve according to claim 8,wherein said optical alignment sleeve is formed of plastics, glass, orzirconia, through which ultraviolet rays or visible light can betransmitted, and wherein said adhesive is of an ultraviolet curing typeor a visible light curing type and has a viscosity of 10,000 cP or moreor is like a gel.
 10. An optical alignment sleeve according to claim 8,wherein said optical alignment sleeve is formed of nondeforming steel,and wherein said adhesive is of a heat-hardening type and has aviscosity of 10,000 cP or more or is like a gel.
 11. An opticalalignment sleeve according to claim 8, 9, or 10, further comprising areinforcing rod extending parallel with said holding sections.
 12. Anoptical alignment sleeve for optical fibers which allows two opticalfibers to be butted against each other for connection, the opticalalignment sleeve comprising: tapered insertion ports through whichoptical fibers are inserted; and holding sections each having a drainsection formed therein so that said optical fiber are inserted throughthe insertion port to discharge an extra portion of an adhesive alreadyfilled in the optical alignment sleeve, to said insertion ports, andwherein said optical fibers are inserted through said insertion ports toallow the extra portion of said adhesive discharged to said insertionports to form fillets.
 13. An optical alignment sleeve according toclaim 12, wherein said optical alignment sleeve is formed of plastics,glass, or zirconia, through which ultraviolet rays or visible light canbe transmitted, and wherein said adhesive is of an ultraviolet curingtype or a visible light curing type and has a viscosity of 10,000 cP ormore or is like a gel.
 14. An optical alignment sleeve according toclaim 12, wherein said optical alignment sleeve is formed ofnondeforming steel, and wherein said adhesive is of a heat-hardeningtype and has a viscosity of 10,000 cP or more or is like a gel.
 15. Anoptical alignment sleeve according to claim 12, 13, or 14, furthercomprising a reinforcing rod extending parallel with said holdingsections.
 16. An optical fiber connecting method comprising: a firststep of inserting optical fibers into an optical alignment sleeve todischarge an extra portion of an adhesive already filled into holdingsections of said optical alignment sleeve, to insertion ports formed atopposite ends of said optical alignment sleeve, via grooves formed insaid holding sections; a second step of inserting said optical fibersinto said optical alignment sleeve to allow the extra portion of saidadhesive discharged to said tapered insertion ports to form fillets; anda third step of solidifying said adhesive to fix said optical alignmentsleeve and said optical fibers.
 17. An optical fiber connecting methodcomprising: a first step of inserting optical fibers into an opticalalignment sleeve to discharge an extra portion of an adhesive alreadyfilled into holding sections of said optical alignment sleeve, toinsertion ports formed at opposite ends of said optical alignmentsleeve, via grooves formed in said holding sections; a second step ofinserting said optical fibers into said optical alignment sleeve toallow the extra portion of said adhesive discharged to said taperedinsertion ports to form fillets; and a third step of solidifying saidadhesive to fix said optical alignment sleeve and said optical fibers.18. An optical fiber connecting device comprising: optical alignmentsleeve holding means for fixing an optical alignment sleeve; and opticalfiber holding means having a clamp that fixes optical fibers in V-typegroove and means for moving said clamp so as to allow said opticalfibers to be inserted into said optical alignment sleeve and buttedagainst each other therein, and wherein said clamp has a fixed coverthat can be closed with said optical fibers temporarily fixed in saidV-type groove formed in a clamp base, using one of the fingers, and saidoptical fibers are sandwiched between said clam base and said fixedcover in said V-type groove.
 19. An optical fiber connecting deviceaccording to claim 18, further comprising a microscope that enablesmagnification of a connection area in which said optical fibers arebutted against each other in said optical alignment sleeve.